The present invention relates to a feed mechanism for hot rolling pilger mills.
Feed mechanisms for pilger rolling mills are usually comprised of a feeder proper which is mounted for movement on a stationary bed and moves a mandrel with a hollow billet in relation to a millstand. The feeder is usually hydraulically advanced and also hydraulically retracted in the direction of rolling. In addition, such feed mechanism includes spindles which are being suitably driven and which meter the individual movement of the feed mechanism during pilger rolling.
Devices of the type described are disclosed, for example, in the German Pat. No. 304,524 as well as in the German Pat. No. 296,673; the former constituting a supplementing improvement over the latter. In accordance with the teaching of these patents it is also known to limit the advance of the feeder through suitable drive mechanism so that the movement cannot be exceeded beyond the prescribed limit. It was already recognized at that time that the rather rough operating conditions during pilger rolling wear greatly on such a mechanical feeder mechanism if its load capacity is exceeded. Ultimately this results through human error generally, and feeding and loading in particular. At that time it was deemed particularly important to avoid strong impacts between feeder and spindle because in these devices these parts do mechanically engage. Also, it was of interest to avoid other damages due to local overload conditions. Such local overload conditions may, for example, occur when the advance is adjusted too large a value or if the dimensions of the hollow billet being rolled were incorrectly predetermined, or if such billet was placed into the machine at too high a temperature.
These drawbacks were attempted to be avoided by providing a releasable stop as between feeder and spindle. It has to be observed, however, that these problems can be solved in that manner only if the principal point to be considered is the avoidance of an impact between spindle and feeder, particularly during preparation of the feeder by the operator. Loads on the spindle during pilger rolling could not be avoided because the known equipment required the operator to take the proper steps for avoiding oveload whenever he deemed it necessary. Also, each decoupling of the connection between the feed mechanism and the spindle amounted to an interruption of the pilger rolling process.
Without any doubt, a mechanically set limit of the advance of the feed mechanism has the advantage of utilizing normal, full capacity for operating the hot rolling pilger mill; and one does not have to worry about disturbances that may result from temporary, excessively large advances. Recently, a proposal has been made (French Pat. No. 1065008) to advance the feeder strictly by mechanical means of a gear rack. An alternative suggestion (French Pat. No. 1165728) proposes the use of a spindle for the principle advance of the feeder. However, the former kind of feeder advance requires an extremely sturdy construction in the gear rack as well as in the gear, the latter proposal requires an extremely sturdy advance spindle because in either case these devices have to take up the entire reaction forces exerted upon them by the feeder. It should be noted that forces may vary direction and may occur in the direction of rolling as well as oppositely thereto. Moreover, the forces may change direction rapidly; clearly such oscillatory forces produce inherently additional wear and unfortunately they introduce additional play which introduces a certain degree of unsteadiness into the position and operation of the feeder device and its advance mechanism. It should be noted, therefore, that purely hydraulically driven feeders do not incur this problem because the hydraulic has an inherently effective resiliency.